[opendtv] Next gen Wi-Fi

  • From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
  • To: "OpenDTV (E-mail)" <opendtv@xxxxxxxxxxxxx>
  • Date: Mon, 5 Jul 2004 18:35:23 -0400

Here's an interesting article. We have discussed the doubling of
IEEE 802.11 bit rates already, but it wasn't clear at the time
how it was going to be accomplished. I had guessed that so-called
space-time codes (ST codes) would have to be used, because more
traditional techniques had already been used in the existing
802.11 standards. Turns out, there are two approaches competing
in the standards process (nothing new for IEEE):

1. Just double the channel bandwidth. Current 802.11a,b,g use
20 MHz bandwidths. So go to 40 MHz.

2. Use ST codes, in what they are nowadays calling MIMO
(multiple input, multiple output). This is where you transmit
the signal on the same channel, but from different antennas at
slightly different times. Then, receive with multiple antennas
and reconstitute the original by applying the appropriate
phase shifts. You can achieve very impressive b/s/Hz numbers
this way. (It's also possible, at the cost of b/s/Hz, to use
only one transmit *or* only one receive antenna, in a
compromised version of this technique.)

ST codes can be implemented with both single frequency and
OFDM techniques. When used with OFDM, each of the subcarriers
is assumed to experience even loss throughout. With single
frequency modulation, of course, this assumption would be
impossible. So from what I've read, ST codes with single
frequency modulation can actually achieve higher spectral
efficiency, although at the cost of receiver complexity.

The goal is to provide at least 100 Mb/s in the WLAN. When
combined with the 802.11 wireless MAC, the usable throughput
is approximately cut in half. But with ST codes, a new MAC
is needed anyway, so that might change.


IEEE pushes WLANs to 'nth' degree

Patrick Mannion
Jul 05, 2004 (9:00 AM)
URL: http://www.commsdesign.com/showArticle.jhtml?articleID=3D22103634

MANHASSET, N.Y. - The IEEE 802.11n task group will start
sorting through 61 proposals for next-generation wireless LANs in
Portland, Ore., next week. The record-setting number of proposals
indicates the importance of the work: a technology stake in the
delivery of high-rate streaming audio, video and data in a
consumer-centric wireless world.

One of the latest entities entering the looming standards battle
is Interuniversity Microelectronics Center (IMEC), the European
research center, which will present its smart-antenna technology
to the so-called TGn task group.

TGn will define a WLAN standard that supports transmission rates
between 100 and 200 Mbits/second, at least double the rate of
current 802.11g/a WLAN standards.

The many proposals fall into two broad camps. One, led by Atheros,
advocates using a 40-MHz bandwidth. Intel, Matsushita, Philips and
Sony join Atheros in this camp, which calls itself TG nSynch. The
competing World Wide Spectrum Efficiency (WWiSE) group, with Airgo
as its leader, is sticking with a 20-MHz bandwidth. Standing with
Airgo are Broadcom, Conexant, Mitsubishi, Motorola,
STMicroelectronics and Texas Instruments.

"One side [TG nSynch] is interested in doubling the bandwidth to
40 MHz and doing more simplistic things on the coding side and
pushing to get 2x to 3x the rates they have now," said Matthew
Shoemake, president of ultrawideband startup WiQuest
Communications Inc., and ex-chairman of the TGn. "The other side
[WWiSE] would like to stay with 20-MHz bands and use more
advanced coding techniques in combination with the MIMO
[multiple-input, multiple-output] techniques."

The standards-setting process is proceeding as usual, said Colin
Macnab, vice president of communications at Atheros
Communications Inc. (Sunnyvale, Calif.), who described group
formation as likely "at a fairly late stage of development."

Robust enough?

Both Shoemake and Macnab said they were aware of the
spectral-efficiency advantages of the single-channel MIMO
approach, but also cited the cost and power issues associated
with multiple RF front ends. Further, Macnab questioned the
robustness of the WWiSE group's spatial-multiplexing techniques.

IMEC said a mix of spatial-division multiplexing, spatial-division
multiple access and space-time block coding is at the core of its
technology. Liesbet Vanderperre, director of wireless-design
technology, said IMEC's 5-GHz MIMO-OFDM proposal balances capacity,
robustness and throughput. The technology is essentially neutral
and can be applied across either camp, she said.

Copyright 2003 CMP Media
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